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The GLAST LAT tracker construction and test
Abstract
GLAST is a next generation high-energy gamma-ray observatory designed for making observations of celestial gamma-ray sources in the energy band extending from 10 KeV to more than 300 GeV. Respect to the previous instrument EGRET, GLAST will have a higher effective area (six times more), higher field of view, energy range and resolution, providing an unprecedented advance in sensitivity (a factor 30 or more). The main scientific goals are the study of all gamma-ray sources such as blazars, gamma-ray bursts, supernova remnants, pulsars, diffuse radiation, and unidentified high-energy sources. The construction and test of the Large Area Telescope (LAT) tracker, has been a great effort during the past years, involving tens of people from many Italian INFN sections and industrial partners. Environmental and performance tests of the hardware, detectors and reading electronics, have been carried on during all the steps of the LAT construction. The resulting LAT performance are better than the ones required by the original science proposal, demonstrating the quality of the italian group effort. In this article we summarize the LAT construction and test workflow, presenting its main results.
. The Gamma-ray Large Area Space Telescope (GLAST) is a mission that is being built by an international collaboration with contributions from space agencies, high-energy particle physics institutes, and universities in France, Italy, Japan, Sweden and the United States to measure the cosmic gamma-ray flux in the energy range 20 MeV to 300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its launch in early 2008, GLAST will open a new and important window on a wide variety of high energy phenomena, including black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations, Lorentz invariance violation, and exotic relics from the Big Bang.
Pulsar observations at high energies, i.e., beyond radio frequencies, shed a different light on the mechanisms at work near
rotating neutron stars. This article assumes that the reader is already convinced that substantially increasing the known
sample of gamma ray pulsars beyond the ̃8 seen with the instruments on the Compton Gamma Ray Observatory (CGRO) is a worthy
goal [36, 63], to focus on how this goal is being pursued.
“Detection” comes in degrees. Simply counting the number of gamma ray excesses positionally coincident with known neutron
stars is useful for population studies, even if source confusion will compromise some associations. Pulsed detection removes
identification ambiguities while bringing precious information about beam geometry via light curve shapes: the EGRET pulsars
mainly have two peaks, with the leading peak slightly offset compared to the single radio peak, and we would like to know
how general this rule is [64]. Accurate determination of the cutoff energy, and, hopefully, the shape of the cut-off, is the
next step. And finally, with enough photon statistics the spectral shape can be broken down by phase-interval. Having these
observables on a large sample of pulsars should allow major steps forward in describing where and how high energy particles
are accelerated.
Results of a phenomenological model to estimate the GRB detection rate by the Fermi Gamma ray Space Telescope are reported. This estimate is based on the BATSE 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV - 5 GeV with EGRET and at 20 keV - 2 MeV with BATSE, and the mean EGRET GRB spectrum for the 5 EGRET spark-chamber GRBs. For a 10% fluence ratio and a number spectral index alpha_1 = -2 at 100 MeV - 5 GeV energies, we estimate a rate of ~ 20 and 4 GRBs per yr in the Fermi Large Area Telescope field of view with at least 5 photons with energy E > 100 MeV and E > 1 GeV, respectively. We also estimate ~ 1.5 GRBs per yr in the Fermi FoV where at least 1 photon with energy E > 10 GeV is detected. For these parameters, we estimate = 1 - 2 GRBs per year detected with the Fermi telescope with more than 100 gamma rays with E >~ 100$ MeV. Comparison predictions for alpha_1 = -2.2, different fluence ratios, and the AGILE gamma-ray satellite are made. Searches for different classes of GRBs using a diagram plotting 100 MeV - 10 GeV fluence vs. 20 keV - 20 MeV fluence is considered as a way to search for separate classes of GRBs and, specifically, spectral differences between the short-hard and long duration GRB classes, and for hard components in GRBs. Comment: 9 pages, 6 figures, Accepted for publication in ApJ; this version contains an additional section that discusses the fluence estimates and uncertainties for EGRET GRBs
The recent discoveries and excitement generated by space satillite experiment EGRET (presently operating on the Compton Gamma Ray Observatory (CGRO)) have prompted an investigation into modern detector technologies for the next generation of space based gamma ray telescopes. The GLAST proposal is based on silicon strip detectors as the “technology of choice” for space application: no consumables, no gas volume, robust (versus fragile), long lived, and self-triggerable. The GLAST detector basically has two components: a tracking module preceding a calorimeter. The tracking module has planes of crossed strip (x, y) 300 μm pitch silicon detectors coupled to a thin radiator to measure the coordinates of converted electron-positron pairs. The gap between the layers (∼ 5 cm) provides a lever arm for track fitting resulting in an angular resolution of < 0.1° at high energy. The status of this R & D effort is discussed including details on triggering the instrument, the organization of the detector electronics and readout, and work on computer simulations to model this instrument.
On April 5, 1991, the Space Shuttle Atlantis carried the Compton
gamma ray observatory (CGRO) into orbit, deploying the satellite on
April 7. The energetic gamma ray experiment telescope (EGRET) was
activated on April 15, and the first month of operations was devoted to
verification of the instrument performance. Measurements made during
that month and in the subsequent sky survey phase have verified that the
instrument time resolution, angular resolution, and gamma ray detection
efficiency were all within nominal limits
The Gamma-ray Large Area Space Telescope (GLAST) is an international and multi-agency space mission that will study the cosmos in the energy range 20 MeV-1 TeV GLAST is an imaging gamma-ray telescope more much capable than instruments flown previously. The main instrument on board of the spacecraft is the Large Area Telescope (LAT), a high energy pair conversion telescope consisting of three major subsystems: a precision silicon tracker/converter, a CsI electromagnetic calorimeter and a segmented anti-coincidence system. In this article, we present the status of the silicon tracker and the improvement on the physics that the silicon can bring in respect to the previous detectors. (C) 2004 Elsevier B.V. All rights reserved.
The Gamma-ray Large Area Space Telescope (GLAST) is an international and multi-agency space mission that will study the cosmos in the energy range 20 MeV – 1 TeV. GLAST is an imaging gamma-ray telescope more much capable than instruments flown previously. The main instrument on board of the spacecraft is the Large Area Telescope (LAT), a high energy pair conversion telescope consisting of three major subsystems: a precision silicon tracker/converter, a CsI electromagnetic calorimeter and a segmented anti-coincidence system. In this article, we present the status of the construction and tests of the silicon tracker.
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